Re: [PATCH] Fix possible alignment issue with dw2-dir-file-name test case

Andreas Arnez
2014-01-17T17:58:38Z

On Thu, Jan 16 2014, Pedro Alves wrote:

> On 01/15/2014 09:33 PM, Edjunior Barbosa Machado wrote:
>>
>
>>> testsuite/
>>> 2014-01-10 Andreas Arnez <arnez@linux.vnet.ibm.com>
>>> Pedro Alves <palves@redhat.com>
>>>
>>> * gdb.dwarf2/dw2-dir-file-name.c (FUNC): Remove "*_start" symbol.
>>> Make "name" extern.
>>> * gdb.dwarf2/dw2-dir-file-name.exp (out_cu, out_line): Replace
>>> references to ${name}_start by references to ${name}.
>>
>> For some reason, the testcase is no longer successful on ppc64 (although it
>> still passes on ppc32): it hits the breakpoints, but no longer shows the
>> filename in none of the tests.
>>
>> From gdb.log:
>> ...
>> (gdb) break compdir_missing__ldir_missing__file_basename
>> Breakpoint 2 at 0x100006c4
>> (gdb) continue
>> Continuing.
>>
>> Breakpoint 2, 0x00000000100006c4 in .compdir_missing.ldir_missing.file_basename ()
>
> Bah, looks like the function's low_pc ends up pointing to the function
> descriptor (because that's what the "name" symbol resolves to in the
> debug info in the .S file)? Looks like we'll need some other solution.

OK, how about this?

----
Subject: [PATCH] Re-introduce '_start' labels and add alignment in dw2-dir-file-name test case.

On ppc64-linux a function symbol does not point to code, but to the
function descriptor. Thus the previous change for this test case
broke it:

https://sourceware.org/ml/gdb-patches/2014-01/msg00275.html

This patch reverts to the original method, re-introducing '_start'
symbols. In addition, it adds sufficient alignment before the label,
such that the label never points into an alignment gap.

testsuite/
2014-01-17 Andreas Arnez <arnez@linux.vnet.ibm.com>

* gdb.dwarf2/dw2-dir-file-name.c (FUNC): Insert alignment and
define "*_start" label. Make "name" static.

* gdb.dwarf2/dw2-dir-file-name.exp: Replace references to
${name} by references to ${name}_start.
---
gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.c | 10 +++++++++-
gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.exp | 6 +++---
2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.c b/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.c
index 2b9cc6a..517df90 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.c
+++ b/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.c
@@ -63,8 +63,16 @@ FUNC (compdir_absolute_ldir_absolute_file_relative_different) \
FUNC (compdir_absolute_ldir_absolute_file_absolute_same) \
FUNC (compdir_absolute_ldir_absolute_file_absolute_different)

+/* Notes: (1) The '*_start' label below is needed because 'name' may
+ point to a function descriptor instead of to the actual code. (2)
+ The '.balign' should specify the highest possible function
+ alignment across all supported architectures, such that the label
+ never points into the alignment gap. */
+
#define FUNC(name) \
- void \
+ asm (".balign 8"); \
+ asm (#name "_start: .globl " #name "_start\n"); \
+ static void \
name (void) \
{ \
v++; \
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.exp b/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.exp
index e523e89..7f29581 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.exp
@@ -54,7 +54,7 @@ proc out_cu { name cu_dir cu_name line_dir line_name } {
.ascii \"GNU C\\0\" /* DW_AT_producer */
.byte 2 /* DW_AT_language (DW_LANG_C) */
.4byte .Lline_${name}_begin /* DW_AT_stmt_list */
- .4byte ${name} /* DW_AT_low_pc */
+ .4byte ${name}_start /* DW_AT_low_pc */
.4byte ${name}_end /* DW_AT_high_pc */
"
if { $cu_dir != "" } {
@@ -65,7 +65,7 @@ proc out_cu { name cu_dir cu_name line_dir line_name } {

.uleb128 3 /* Abbrev: DW_TAG_subprogram */
.asciz \"${name}\" /* DW_AT_name */
- .4byte ${name} /* DW_AT_low_pc */
+ .4byte ${name}_start /* DW_AT_low_pc */
.4byte ${name}_end /* DW_AT_high_pc */

.byte 0 /* End of children of CU */
@@ -122,7 +122,7 @@ proc out_line { name cu_dir cu_name line_dir line_name } {
.byte 0 /* DW_LNE_set_address */
.uleb128 5
.byte 2
- .4byte ${name}
+ .4byte ${name}_start
.byte 1 /* DW_LNS_copy */
.byte 3 /* DW_LNS_advance_line */
.sleb128 1 /* ... to 1000 */
--
1.7.1